"We emailed her some stuff and she wrote to it, too. So it was like Courtney kind of doing Fall Out Boy, letting rip, which was cool. When was the last time people heard Courtney like that? It's cool for people to remember she's not just a celebrity."

Fall Out Boy guitarist Joe Trohman concurs: "Like her or not, Courtney has a punk rock attitude and aggression that's so cool."

The band also collaborated with Sir Elton John on a track on their comeback album, which has since become their highest charting release to date.

Pete was in awe of the British pop legend.

"The part where Elton sings, 'Rock and roll,' he sings it like someone who has really experienced it," Pete said in reference to Elton's work on the album's title track.

"It was so crazy to have him on it," enthused Pete's bandmate Patrick Stump.

"He got the song, he got the record, and he was really important in encouraging us on the album title and everything we were trying to do."